Effects of Lespedeza cuneata invasion on tallgrass prairie plant and arthropod communities

We examined effects of the invasive species Lespedeza cuneata on native plants and foliar arthropod communities in a tallgrass prairie. Through observational and manipulative experiments, we examined plant and arthropod responses to L. cuneata over one growing season. The observational study found little impact of the invasive plant on arthropods. By the end of the manipulative experiment, the combined biomass of native grasses and forbs was reduced by approximately 50% in Lespedeza-present plots, while total arthropod numbers were only about 15% lower. Seasonal differences were evident; L. cuneata-absent plots showed lower arthropod numbers in May, but higher abundances in June. Some feeding groups, notably carnivorous arthropods, appeared unaffected by L. cuneata. We tested three hypotheses (one bottom-up and two top-down processes) to explain the relatively weak response of the arthropod community to the invasive plant. Nitrogen content of native plants adjacent to L. cuneata areas was significantly higher compared to plants more distant. Ground arthropod predators were higher during mid-summer in L. cuneata areas, which may partially explain seasonal variation in foliar arthropods. Insectivorous birds were unaffected by L. cuneata abundance, suggesting that arthropod predation rates by birds are unchanged. We suggest that while L. cuneata has strong effects on native plants, its ability to increase neighboring plant quality compensates for the lower biomass of native plants in L. cuneata areas, moderating the arthropod response. While management of this invasive species remains a priority, tallgrass prairie food webs may be partly resistant to L. cuneata invasion.